Indirect evidence implicates a virus in the etiology of Multiple Sclerosis (MS) and more direct evidence shows that viruses cause other human demyelinating diseases. Coronavirus mouse hepatitis virus (MHV) infection of mice is a good model system for the study of virus-induced chronic demyelination. The long term goal of this project is to use the techniques of molecular biology to understand the mechanisms of persistent infection and virus-induced chronic CNS disease in this animal model. We have previously shown that intracerebral inoculation of MHV-A59 into 4-6 week old C57BL/6 mice results in chronic CNS disease in 100% of the animals with very little acute disease or mortality. Primary demyelination can be detected as late as six months post infection and can be enhanced by immunosuppression. While infectious virus and viral antigens cannot be detected during the chronic disease state, viral nucleic acids do persist. In this proposal we will study the mechanism of viral persistence and its relationship to demyelination. Using in situ hybridization and gene-specific cloned MHV-A59 cDNAs as probes to detect viral nucleic acids and immunoperoxidase staining with antisera directed against individual viral proteins we will determine if part or all of the viral genome is expressed at the transcriptional and translational levels. Cyclophosphamide treatment will be carried out to determine if virus can be recovered from chronically infected animals that have been immunosuppressed. Viral tropism will be studied by carrying out infections in vitro in enriched oligodendrocyte cultures. As a more secondary goal we will investigate the possible relationship between human coronaviruses and MS. We will use the highly specific and sensitive technique of nucleic acid hybridization to probe for coronavirus sequences in the CNS of MS patients. Thus, in situ hybridization of CNS autopsy tissue from MS patients will be carried out using cloned DNA fragments homologous to human coronavirus genomes as probes.